Method for preparing sintered annular nuclear fuel pellet

Abstract

A method for fabricating a sintered annular nuclear fuel pellet includes molding nuclear fuel powder or granule, an oxide of a fissile element (M), to fabricate an annular nuclear fuel green body. A rod-like shaped structure is inserted into the annular nuclear fuel green body and sintered in a slight oxidizing gas atmosphere such that the oxide of the fissile element has a balanced O/M ratio higher than a desired O/M ratio (oxygen/fissile element) of a final sintered annular nuclear fuel pellet, while being maintained in a cubic phase. The sintered annular nuclear fuel pellet is then reduced in a reductive gas atmosphere so as to have the desired O/M ratio in the state that the rod-like shaped structure is inserted.

What is claimed is: 
     
       1. A method for fabricating a sintered annular nuclear fuel pellet, the method comprising:
 pressing nuclear fuel powder or granule, an oxide of a fissile element (M), to fabricate an annular nuclear fuel green body; 
 inserting a rod-like shaped structure into the annular nuclear fuel green body; 
 sintering the rod-like shaped structure-inserted annular nuclear fuel green body in an atmosphere of a slight oxidizing gas such that the oxide of the fissile element has a balanced O/M ratio higher than a desired O/M ratio (oxygen/fissile element) of a final sintered annular nuclear fuel pellet, while being maintained in a cubic phase; 
 reducing the sintered annular nuclear fuel pellet in a reductive gas atmosphere so as to have the desired O/M ratio in the state that the rod-like shaped structure is inserted, whereby a gap is formed between the rod-like shaped structure and the sintered annular nuclear fuel pellet; and 
 separating the rod-like shaped structure from the reduced sintered annular nuclear fuel pellet. 
 
     
     
       2. The method of  claim 1 , wherein the oxide of the fissile element is uranium oxide, the desired O/M ratio and the balanced O/M ratio are a desired O/U (oxygen/uranium) ratio and a balanced O/U, respectively. 
     
     
       3. The method of  claim 2 , wherein the desired O/U ratio of the sintered annular nuclear fuel pellet ranges from 2.00 to 2.02. 
     
     
       4. The method of  claim 3 , wherein the balanced 0/U ratio of the nuclear fuel green body sintered in the slight oxidizing gas atmosphere ranges from 2.1 to 2.25. 
     
     
       5. The method of  claim 1 , wherein the rod-like shaped structure is made of a metal material. 
     
     
       6. The method of  claim 5 , wherein the rod-like shaped structure is made of an INCONEL®-based alloy. 
     
     
       7. The method of  claim 1 , wherein the rod-like shaped structure is made of a ceramic material. 
     
     
       8. The method of  claim 7 , wherein the rod-like shaped structure comprises at least one ceramic material selected from the group consisting of ZrO 2 , ThO 2 , MgO, Al 2 O 3 , SiC, Si 3 N 4 , and graphite. 
     
     
       9. The method of  claim 1 , wherein a diameter of the rod-like shaped structure is less than the inner diameter of the annular nuclear fuel green body and the diameter of the rod-like shaped structure is the same as or larger than the largest inner diameter of an equivalent sintered annular nuclear fuel pellet if sintered under the same conditions as the sintered annular nuclear fuel pellet of  claim 1  except in a state that the rod-like shaped structure is not inserted. 
     
     
       10. The method of  claim 1 , wherein the slight oxidizing gas is at least one selected from the group consisting of carbon dioxide, water vapor, and inert gas. 
     
     
       11. The method of  claim 1 , wherein the reductive gas is a hydrogen gas. 
     
     
       12. The method of  claim 1 , wherein the sintering of the annular nuclear fuel green body is performed at a temperature ranging from 1,000 degrees Celsius to 1,500 degrees Celsius. 
     
     
       13. The method of  claim 1 , wherein the reducing of the sintered annular nuclear fuel pellet is performed at a temperature ranging from 500 degrees Celsius to 1,500 degrees Celsius. 
     
     
       14. The method of  claim 1 , wherein the nuclear fuel powder or granule is an oxide of at least one fissile element selected from the group consisting of uranium, plutonium, and thorium.